1. Field of the Invention
The present invention relates to a method for estimating quantities that represent the state of a vehicle, such as the vehicle body sideslip angle.
2. Description if the Related Art
Conventionally, control is known for improving the maneuverability of a vehicle by using the quantities that represent the vehicle state, such as the vehicle body sideslip angle xcex2 (that is, the angle formed between the forward direction of the vehicle and the longitudinal axis of the vehicle) when controlling the state of movement of the vehicle during a turning movement, for example. In this type of control, a method is known wherein, in the case that, for example, the vehicle body sideslip angle xcex2 is used, the yaw rate r detected by a yaw rate sensor (that is, the turn angle speed of the vehicle center of gravity around the axis in the vertical direction), the lateral acceleration Gy detected by the lateral acceleration sensor (that is, the acceleration or deceleration added in the lateral direction of the vehicle), and the velocity V of the vehicle (vehicle speed) detected by the vehicle velocity sensor are substituted into the following equation 1, which is derived from the equation representing the physical relations of the quantities that represent the state of the movement of the vehicle, and by carrying out integration with respect to time, the vehicle body sideslip angle xcex2 is estimated.
However, in methods in which the results of the detected quantities from each of the sensors are integrated with respect to time, the influence of noise in each of the sensors, the error included in the results of the detected quantities, and the deviations in the calibrations of each of the sensors accumulate, and thus there is the concern that the precision of the estimation of the vehicle body sideslip angle xcex2 deteriorates.                     β        =                  ∫                                    (                                                                    G                    y                                    V                                -                r                            )                        ⁢                          ⅆ              t                                                          Eq        .                  xe2x80x83                ⁢        1            
In response to these problems, the method of estimating the vehicle body sideslip angle and estimating apparatus disclosed, for example, in Japanese Unexamined Patent Application, First Publication, No. Hei 11-78933, is known. In this method, models of a plurality of wheels are introduced, and the vehicle body sideslip angle xcex2 is estimated by switching the model for the wheels depending on, for example, the case that the coefficient of friction of the road surface changes or the various conditions during travel in the critical vicinity of movement of the vehicle (that is, the critical zone in which there is the possibility that the state of movement of the vehicle may become unstable when there is no control of any kind).
However, in the vehicle body sideslip angle estimation method and estimation apparatus according to the example of conventional technology described above, there are the problems that the computation processing of the vehicle body sideslip angle xcex2 becomes complicated, and that the computation load increases.
Furthermore, there are cases in which the estimated value of the vehicle body sideslip angle xcex2 drastically changes due to the timing during which the models of a plurality of wheels are switched, and thus the there is a concern that the drivability will deteriorate.
In consideration of the problems described above, it is an object of the present invention to provide a method of estimating the quantities representing the state of the vehicle that can improve the precision of the estimations of the vehicle body sideslip angle or values related to the vehicle body sideslip angle by a simple and inexpensive method.
In order to solve the problems and attain the objects described above, a first aspect of the method of estimating quantities that represent the state of the vehicle of the present invention comprises a step of detecting the yaw rate and vehicle speed (for example, step S 02 and step S 06 in the embodiment described below); and a step (for example, step S 02 to step S 03 in the embodiment described below) of calculating three equations which comprises an equation of equilibrium (for example, equation 2 in the embodiment described below) for the force in the lateral direction of the vehicle, an equation of equilibrium (for example, equation 3 in the embodiment described below) for the moment around the vertical axis of the vehicle, and an equation for the physical relationships of the quantities that represent the state of the vehicle movement (for example, equation 4 in the embodiment described below), using the vehicle body sideslip angle, the front wheel cornering power, and the rear wheel cornering power as unknown values.
According to the first aspect of the present invention, the method of estimating the quantities that represent the vehicle state described above, based on an equation of equilibrium for the force in the lateral direction of the vehicle, an equation of equilibrium for the moment around the vertical axis of the vehicle, and an equation for the physical relationships of the quantities that represent the state of the vehicle movement obtained from a predetermined model of the movement of the wheels that describes the yaw movement of the vehicle in, for example, a two wheel model, it is possible to derive simultaneous equations comprising the three unknown quantities of the vehicle body sideslip angle, the front wheel cornering power, or the rear wheel cornering power by setting detected values from each of the sensors to the yaw rate and the vehicle speed. That is, it is possible to estimate the vehicle sideslip angle using a simple method that limits increases in the computing load and has high precision by using the exact number of equations for the number of unknowns to be calculated.
The second aspect of the present invention provides a method of estimating quantities that represent the vehicle state comprises a step (for example, steps 02 and step S 06 in the embodiment described below) of detecting the yaw rate, the lateral acceleration, and the vehicle speed, a step (for example, step S 02 to step S 08 in the embodiment described below) of calculating the velocity of the vehicle in the lateral direction using three equations, an equation of equilibrium for the force in the lateral direction of the vehicle (for example, equation 15 in the embodiment described below), an equation of equilibrium for the moment around a vertical axis of the vehicle (for example, equation 16 in the embodiment described below), and an equation for the physical relationships of the quantities that represent the state of the vehicle movement, using the vehicle speed in the lateral direction, the front wheel cornering power, and the rear wheel cornering power as unknown values, and a step (for example, step S 04 in the embodiment described below) of calculating the vehicle body sideslip angle from the velocity of the vehicle in the lateral direction.
According to the second method of estimating the quantities that represent the state of a vehicle of the present invention, based on an equation of equilibrium for the force in the lateral direction of the vehicle, an equation of equilibrium for the moment around the vertical axis of the vehicle, and an equation for the physical relationships of the quantities that represent the state of the vehicle movement obtained from a predetermined movement model of vehicles that describes the yaw movement of the vehicle in, for example, a two wheel model, it is possible to derive simultaneous equations comprising three unknown quantities that represent the speed of the vehicle in the lateral direction, the front wheel cornering power, and the rear wheel cornering power by setting detected values from each of the sensors to the yaw rate and the vehicle speed. Here, it is possible to estimate the vehicle body sideslip angle using a simple method that limits increases in the computation load while at the same time has a high precision because it is possible to calculate unambiguously the vehicle body sideslip angle from the velocity of the vehicle in the lateral direction and the vehicle speed.
A third aspect of the present invention provides a method of estimating the quantities that represent the state of a vehicle of the present invention comprises: a step (for example, steps 02 and step S 06 in the embodiment described below) of detecting the yaw rate, the lateral acceleration, and the vehicle speed, and a step (for example, step S 02 to step S 08 in the embodiment described below) of calculating the vehicle body sideslip angle using three equations comprising an equation of equilibrium for the force in the lateral direction of the vehicle (for example, equation 13 in the embodiment described below), an equation of equilibrium for the moment around a vertical axis of the vehicle (for example, equation 12 in the embodiment described below), and an equation for the physical relationship of the quantities that represent the state of the vehicle movement (for example, equation 4 in the embodiment described below), using the vehicle body sideslip angle, the front wheel tires lateral force, and the rear wheel tire lateral force as unknowns values.
According to the third method of estimating the quantities that represent the state of a vehicle of the present invention, based on an equation of equilibrium for the force in the lateral direction of the vehicle, an equation of equilibrium for the moment around the vertical axis of the vehicle, and an equation for the physical relationships of the quantities that represent the state of the vehicle movement obtained from a predetermined movement model of vehicles that describes the yaw movement of the vehicle in, for example, a two wheel model, it is possible to derive simultaneous equations comprising the three unknown quantities that represent the vehicle body sideslip angle, the front wheel tires lateral force, and the rear wheel tires lateral force by setting detected values from each of the sensors to the yaw rate, the lateral acceleration, and the vehicle speed. Here, it is possible to estimate the vehicle body sideslip angle using a simple method that limits increases in the computation load while at the same time has a high precision.
The fourth aspect of the present invention provides a method of estimating the quantities that represent the state of a vehicle of the present invention comprises: a step (for example, step S 02 and S 06 in the embodiment described below) of detecting the yaw rate (for example, the yaw rate r in the embodiment described below), the lateral acceleration (for example, the lateral acceleration Gy in the embodiment described below), and the vehicle speed (for example, the vehicle speed V in the embodiment described below), and a step (for example, step S 02 to step S 08 in the embodiment described below) of calculating the values related to the vehicle sideslip angle using three equations, the equation of equilibrium for the force in the lateral direction of the vehicle (for example, equation 2, equation 11, and equation 15 in the embodiment described below), the equation for equilibrium of the moment of the vehicle around a vertical axis (for example, equation 3, equation 12, or equation 16 in the embodiment described below), and an equation for the physical relationships between the quantities that represent the state of the vehicle movement (for example, equation 4 and equation 19 in the embodiment described below), having as unknowns values related to the vehicle body sideslip angle (for example the vehicle body sideslip angle xcex2 or the Vy component of the vehicle speed V in the lateral direction in the embodiment described below), the variables that determine the characteristics of the front wheel tires (for example, the front wheel cornering power Kf and coefficient of friction xcexc in the embodiment described below), and the variables that determine the characteristics of the rear wheels (for example, the rear wheel cornering power Kr and the coefficient of friction xcexc in the embodiment described below).
According to the fourth method of estimating the quantities that represent the state of a vehicle based on three equations, equation of equilibrium for the force in the lateral direction of the vehicle, an equation of equilibrium for the moment around the vertical axis of the vehicle, and an equation for the physical relationships of the quantities that represent the state of the vehicle movement, obtained from a predetermined movement model of vehicles that describes the yaw movement of the vehicle in, for example, a two wheel model, it is possible to derive simultaneous equations comprising the three unknown quantities that represent the values related to the vehicle body sideslip angle, the variables that determine the characteristics of the front wheel tires, and the variables that determine the characteristics of the rear wheel tires by setting detected values from each of the sensors to the yaw rate, the lateral acceleration, and the vehicle speed. That is, it is possible to estimate the values related to the vehicle body sideslip angle using a simple method that limits increases in the computation load while at the same time has a high precision by using only the exact number of equations necessary for the number of unknowns to be calculated.
The fifth aspect of the present invention provides a method of estimating the quantities that represent the state of the vehicle comprises: a step (for example, step S 05 in the embodiment described below) of calculating the differential values (for example, the vehicle body sideslip angle differential value xcex2xe2x80x2 and the differential value Vyxe2x80x2 in the embodiment described below) of the values related to said vehicle sideslip angle based on said yaw rate and said vehicle speed, and a step (for example, step S 06 in the embodiment described below) of testing the differential value of the values related to said vehicle body sideslip angle by said lateral speed.
According to the fifth method of estimating the quantities that represent the state of a vehicle described above calculates the differential values of the values related to the vehicle body sideslip angle by substituting the detected values of the yaw rate and the vehicle speed input from each of the sensors into two equations comprising the equation of equilibrium for the force of a vehicle in the lateral direction and the equation of equilibrium for the moment around a vertical axis of the vehicle.
In addition, based on the differential values of the values related to the calculated vehicle body sideslip angle, the estimated value of the lateral acceleration is calculated by the equation representing the physical relationships of the quantities that represent the vehicle movement, and by comparing this estimated value with the detected value of the lateral acceleration output, for example, by sensors or the like, the differential values of the values related to the vehicle sidestep angle.
In this case, compared to the case of comparing the physical quantities calculated based on the vehicle body sideslip angle obtained by integrating with respect to time the differential value of the values related to the vehicle body sideslip angle, it is possible to prevent errors from accumulating due to the integration computations of variables that are the object of testing, and the testing can be executed with a high precision.
The sixth aspect of the method of estimating the quantities that represent the state of a vehicle of the present invention comprises: a step (for example, step S 04 in the embodiment described below) of calculating the values related to said vehicle body sideslip angle by integrating the differential values of said values related to the vehicle body sideslip angle, and a step (for example, step S 03 in the embodiment described below) of calculating the differential values of the said values related to the vehicle sideslip angle in the present processing by using said values related to the vehicle sideslip angle calculated in the previous processing.
According to the sixth method of estimating the quantities that represent the state of a vehicle described above, when calculating the differential values of the values related to the vehicle body sideslip angle, by using the values related to the vehicle body sideslip angle calculated in the previous processing, recursive calculation processing is carried out, and thereby it is possible to prevent the values related to the vehicle body sideslip angle obtained by integrating with respect to time the differential values of the values related to the vehicle body sideslip angle from diverging.
That is, by repeating the recursive processing, the values related to the vehicle body sideslip angle converge, and thus drastic fluctuations in the estimated values of the values related to the vehicle body sideslip angle can be avoided, and the stability of the vehicle behavior control can be guaranteed.
In addition, the seventh aspect of the method of estimating the quantities that represent the state of a vehicle comprises the step (for example, step S 01) in the embodiment described below) of eliminating either said variables that determine the characteristics of the front wheel tires or said variables that determine the characteristics of the rear wheel tires from said equation of equilibrium for the force in the lateral direction of the vehicle and said equation of equilibrium for the moment around a vertical axis of the vehicle.
According to the seventh method of estimating the quantities that represent the state of a vehicle, an equation is calculated from which either the variables that determine the characteristics of the front wheel tires or the variables that determine the characteristics of the rear wheel tires have been eliminated from the equation of equilibrium for the force in the lateral direction of the vehicle and the equation of equilibrium for the moment around a vertical axis of the vehicle. In addition, the differential values of the values related to the vehicle sideslip angle are calculated based on an equation obtained by solving this equation for the differential values of the values related to the vehicle body sideslip angle.
In this case, by estimating the values related to the vehicle body sideslip angle and either the variables that determine the characteristics of the front wheel tires or the variables that determine the characteristics of the rear wheel tires, in comparison to the case of estimating, for example, three unknowns, the computing load can be decreased.
Furthermore, the eighth aspect of the method for estimating the quantities representing the state of a vehicle comprises: a step (for example, step S 01 to step S 03 in the embodiment described below) of calculating the differential values of said values related to the vehicle body sideslip angle by providing initial values to either said variables that determine the characteristics of the front wheel tires or said variables that determine the characteristics of the rear wheel tires, whichever has not been eliminated, a step (for example, step S 05 in the embodiment described below) of calculating the lateral acceleration (for example the estimated lateral acceleration Gye of the vehicle) from an equation that represents the physical relationships of the of said state of the vehicle movement using the differential values of said values related to the vehicle sideslip angle, and a step (for example, step S 08 in the embodiment described below) that updates said initial values based on the results of comparing said calculated lateral acceleration and said detected lateral acceleration.
According to the eighth method of estimating the quantities that represent the state of a vehicle described above, depending on the results of comparing the estimated value of the lateral acceleration calculated based on the differential values of the values related to the vehicle body sideslip angle in the previous processing and the detected value of the lateral acceleration input by sensors, either the variables that determine the characteristics of the front wheel tires or the variables that determine the characteristics of the rear wheel tires, which are input when calculating the differential values of the values related to the vehicle body sideslip angle in the present processing, are updated. Thereby, depending, for example, on the changes in the road surface or the like, even in the case that the variables that determine the characteristics of the front wheel tires or the variables that determine the characteristics of the rear wheel tires fluctuate drastically, it is possible to suitably calculate the differential values of the values related to the vehicle body sideslip angle.